Seeing by starlight, more precisely than ever

Mark Marlow Mead, a volunteer captain for a search and rescue team in Calaveras County, in Northern California, got the call on an August evening three summers ago.

A hiker had come across a couple, and the woman was in distress, suffering from a severe allergic reaction. Her husband didn't want to move her alone. The hiker had told them he'd send help, but he couldn't remember exactly where they were located — just that they were on a large reservoir that was seven miles long. And it was already nighttime.

Mr. Mead and two other men went to the reservoir and set out in a motorboat. Along with their rescue supplies they also had a secret weapon: night-vision goggles manufactured by ITT Industries, a technology company based in White Plains. Since the goggles can amplify light up to 50,000 times, Mr. Mead could see even the smallest speck of light glowing out at him across the water.

Sure enough, when he was two miles into the reservoir he saw a light up ahead. Soon the team had located the campsite, dispensed medical treatment and brought the couple back.

"Using night vision we were able to see the campers right away instead of having to do a shoreline search for another five miles," said Mr. Mead. "It would've taken four to six hours instead of the 15 minutes that it actually took."

Search and rescue groups like Mr. Mead's, the military, law enforcement agencies and outdoors enthusiasts are all using night-vision technology to literally see in the dark. Although night vision is not new — it has been around in basic form since World War II — improvements in the technology are continually being made.

There are three versions of light-amplifying night-vision technology available. Generation 1, the oldest and also the cheapest, is designed for the sports and gadget enthusiast. It can be purchased at sporting goods stores and specialty shops and online, and costs between $100 and $600, depending on the model. The second and third generations, which produce sharper images in much lower light, cost from $2,500 to more than $10,000. While some models are sold for civilian use, in general they are used by the military and law enforcement agencies.

All of the types work by converting photons of light into electrons, multiplying them and then converting the electrons back into photons.

The second- and third-generation technologies benefit from use of a microchannel plate — essentially, glass with millions of microscopic holes in it — to multiply the electrons.

"By the time one electron goes in, 10,000 to 20,000 electrons come out of each channel," said Jeff Slusher, vice president of business development for Northrop Grumman Electro- Optical Systems, a maker of night-vision equipment based in Garland, Tex. The third generation goes even further, using a more efficient and sensitive cathode, which converts more photons into electrons. In all generations of equipment, images appear against a green background, so users can switch from night vision to regular vision without waiting for their eyes to adjust to the change. This means that colors are often incorrect.

"A white shirt could look black through night vision, so we need to teach law enforcement how to use the technology," said Jim Harris, vice president of engineering for ITT Technologies.

Consumers need education, too. "Night-vision goggles limit your peripheral vision," said Jack O'Dell, a spokesman for the Coast Guard in Washington. "You'd better know how to interpret what you're seeing before you put them on and go out boating at night. If a boat is approaching you from the side, you might not even see it."

Another kind of equipment uses sensors that detect light at infrared wavelengths, outside the visible range. Objects warmer than their surroundings emit more infrared light, so people, animals or warm objects appear as lighter images with infrared goggles.